Chain dynamics in entangled polymers: Power laws of the proton and deuteron spin-lattice relaxation dispersions

Abstract

Chain modes of entangled polymer melts can directly be probed in a frequency range 102 Hz<ν<108 Hz with the aid of field-cycling proton or deuteron relaxometry. The frequency dispersion of proton spin-lattice relaxation universally shows crossovers between the power laws T1∝ν0.5±0.05 (region I), T1∝ν0.25±0.05 (region II), and T1∝ν0.45±0.05 (region III) from high to low frequencies. Regions I and II are identified as limits of a theory based on the renormalized Rouse model assuming intrasegment dipolar interactions. Region III does not appear in distinct form in the deuteron T1 dispersion of perdeuterated chains. It is inferred that proton relaxation in region III is influenced by intersegment interactions which are negligible with deuterons. A corresponding formalism is given. The comparison with the experimental data suggests some multi-chain correlation of the displacement dynamics.